1. Field of the Invention
The present invention generally relates to a shock wave generating apparatus capable of disintegrating an object within a biological object under medical examination, e.g., a cancer cell, and a concretion by utilizing focused energy of shock waves. More specifically, the present invention is directed to a shock wave generating apparatus capable of generating a wide concretion-disintegrating region by employing ring-shaped transducers, and also to a hyperthermia curing system.
2. Description of the Prior Art
Various types of shock wave generating apparatuses have been proposed, such as those described in Japanese KOKAI (Disclosure) patent application No. 62-49843 (1987). In FIG. 1, for example, there is shown, a sectional view of an ultrasonic wave applicator of one conventional shock wave generating apparatus.
The construction of this ultrasonic wave applicator 1 is as follows. A through hole having a predetermined shape is formed in a center portion of the applicator 1. A vibrating element (e.g., a piezoelectric transducer element) 2 is spherically formed and a backing material 3 is uniformly adhered to a rear surface of this spherical vibrating element 2. An imaging ultrasonic probe 4 is positioned in such a manner that a transmitting/receiving wave front (ultrasonic array) 4a is located at the curved surface which is identical to the shock wave transmitting/receiving wave front of the vibrating element 2, or rearward of the aforementioned wave front. Furthermore, this ultrasonic wave applicator 1 includes a water bag 5 containing water as a coupling medium for the ultrasonic waves. Reference numeral 8 indicates a biological body under medical examination.
To disintegrate a concretion or calculus within a biological body by utilizing the above-described conventional shock wave generating apparatus, the focal point of the generated shock wave must be pointed to this concretion, which action will hereinafter be referred to as "a positioning of a focal point". As apparent from FIG. 2A, a shape of this focal point is very small, like a "pinpoint focused region".
FIG. 2A to 2C illustrate relationships between the shock wave front and focused region in the conventional shock wave generating apparatus shown in FIG. 1.
In FIG, 2A, reference numeral 7 indicates a single focused region of the shock wave transmitted from the vibrating element 2. This vibrating element 2 is subdivided into six portions as illustrated in FIG. 2B, and the six positions are arranged in a spherical form as represented in FIG. 2A. It should be noted that only one focused region 7 is formed from six element portions "a" to "f". FIG. 2C is an illustration of the focused region 7 as viewed from the transmission direction of the shock wave toward an object 8 to be disintegrated.
Assuming now that an area indicative of a half value of a peak pressure produced by a shock wave transmitted from a vibrating element is defined as the above-described pinpoint focused region .tau., this single focused region 7 is geometrically determined by the diameter of the spherical body and the aperture of the vibrating element 2. As apparent from FIG. 2C, Since a size of this pinpoint focused region 7 is very small as compared with the object 8 to be disintegrated within the biological body, the calculus disintegrating efficiency by the shock wave is considerably lowered, which necessarily requires a large quantity of time so as to completely disintegrate the object 8.
To solve the above-described problem (i.e., lengthy disintegrating time) associated with such a prior art shock wave generating system, very recently, a very novel and epoch-making shock wave generating system has been patented under U.S. Pat. No. 5,062,412 on Nov. 5, 1981 to Okazaki entitled "SHOCK WAVE GENERATING APPARATUS FORMING WIDE CONCRETION-DISINTEGRATING REGION BY FOCUSED SHOCK WAVE".
Simply speaking, in accordance with this U.S. Patent, a wide focused region is formed by energizing a plurality of transducers in such a manner that a plurality of pinpoint focal points are formed and positioned adjacent to each other.
The featured structure of this U.S. Patent will now be summarized with reference to FIGS. 3A to 3C.
Referring now to FIGS. 3A to 3C, the shock wave generating means 15 will be described in detail. FIGS. 3A to 3C pictorially represent the relationships between the shock wave front and the focused regions in the shock wave generating apparatus. As illustrated in FIGS. 3A and 3B, this shock wave generating means 15 is constructed in such a manner that a plurality of ultrasonic vibrating elements, e.g., 14 pieces of the piezoelectric transducer elements are arranged in an endless form, and the wave front of the generated shock wave is a substantially spherical shape. The shock wave generating means 15 includes a plurality of vibrating element groups, e.g., 7 groups, from which the geometrically focused shock waves are produced. That is to say, a first vibrating element group 10a is formed by one pair of vibrating elements denoted by "a" in FIG. 3B; a second vibrating element group 10b is formed by a pair of vibrating elements indicated by "b" in FIG. 3B a sixth vibrating element group 10f is constructed of a pair of vibrating elements denoted by "f" shown in FIG. 3B; and furthermore a seventh vibrating element 10g group is formed by one pair of vibrating elements denoted by "g" shown in FIG. 3B. As illustrated in FIG. 3B, one pair of vibrating elements "a" to "g" constituting the respective vibrating element groups 10a to 10g are positioned on diagonal lines. It should be noted that for the sake of the simplicity, arrows for denoting the respective vibrating element groups 10b to 10g are attached only to one vibrating element constructing the respective element groups.
The vibrating elements for producing the shock waves, may for instance, be a piezoelectric transducer elements.
FIG. 3C illustrates the respective focused regions which are simultaneously formed by driving the vibrating element groups 10a to 10g, as viewed in the shock wave transmission direction. It should be noted that although the shapes of these focused regions are circular, the actual shapes thereof are elliptic or oval.
As previously described, one pair of vibrating elements "a" and "a" constituting the first vibrating element group 10a are positioned in such a manner that the shock waves transmitted from these vibrating elements "a" and "a" are synthesized at a first position geometrically defined so as to form a first focused region 11a. Another pair of vibrating elements "b" and "b" constituting the second vibrating element group 10b are positioned in such a manner that the shock waves transmitted from these vibrating elements "b" and "b" are synthesized at a second position geometrically defined, thereby forming a second focused region 11b. Similarly, the respective vibrating elements for constituting the third, fourth, fifth, sixth and seventh vibrating element groups 10c, 10d, 10e, 10f, and 10g are so arranged as to form third to seventh focused regions 11c to 11g, respectively, at geometrically defined areas. These focused regions 11a to 11g are formed at the same time under the condition that the simultaneously formed focused regions are juxtaposed with each other, as illustrated in FIG. 3C. As a consequence, a synthesized effective focused region by the first through seventh focused regions 11a to 11g is about 7 times larger than each of these focused regions 11a to 11g. In other words, since the resultant effective focused region simultaneously formed by juxtaposing a plurality of focused regions 11a to 11g with each other can be made considerably larger than the pinpoint focal point 7 (see FIG. 2C) formed in the shock wave generating apparatus previously described. The effective disintegrating efficiency for the object to be disintegrated can thus be improved according to this U.S. Patent.
However, the above-described U.S. Patent has a lack of practical utilization. First, the same number of delay circuits, e.g., 7 delay circuit groups, are required as that of the transducer channels, resulting in a very complex delay control. Secondly, it is desirable from a practical standpoint that a calculus-disintegration treatment should be performed with irradiating shock waves having an optimum beam width (i.e., a size of a focused region along an aperture direction) relative to the calculus, taking account of various conditions of this calculus. Also, to disintegrate a calculus or stone, a peak pressure of shock wave pulses, or a temperature of focused energy of a continuous wave must be set to be higher than a threshold value. Nevertheless, if an excessive peak pressure is administered to a biological body, it may feel pain and may incur medical risk.
Furthermore, sizes of a focused region are preferably varied along not only an aperture direction, but also a depth direction in such a wide focused region type shock wave generating system, or hyperthermia curing system.